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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 58, NO. 8, AUGUST 2011 3373

A Novel VSI- and CSI-Fed Dual Stator InductionMotor Drive Topology for Medium-Voltage

Drive ApplicationsKamalesh Hatua and V. T. Ranganathan, Senior Member, IEEE

AbstractA new configuration is proposed for high-power in-duction motor drives. The induction machine is provided with twothree-phase stator windings with their axes in line. One winding isdesigned for higher voltage and is meant to handle the main (ac-tive) power. The second winding is designed for lower voltage andis meant to carry the excitation (reactive) power. The excitationwinding is powered by an insulated-gate-bipolar-transistor-basedvoltage source inverter with an output filter. The power windingis fed by a load-commutated current source inverter. The com-

mutation of thyristors in the load-commutated inverter (LCI) isachieved by injecting the required leading reactive power from theexcitation inverter. The MMF harmonics due to the LCI currentare also cancelled out by injecting a suitable compensating com-ponent from the excitation inverter, so that the electromagnetictorque of the machine is smooth. Results from a prototype driveare presented to demonstrate the concept.

Index TermsActive reactive induction machine (ARIM), load-commutated inverter (LCI), medium-voltage drive, synchronousmachine.

NOMENCLATURE

NR Equivalent rotor number of turns.

iR Equivalent rotor current.NP Equivalent power winding num-ber of turns.

iP Equivalent power windingcurrent.

NF Equivalent excitation windingnumber of turns.

iF Equivalent excitation windingcurrent.

ESP Equivalent back electromotiveforce (EMF) of power winding.

ESF Equivalent back EMF of excita-tion winding.

ER Equivalent back EMF of rotorwinding.

P Flux developed by the powerwinding.

R Flux developed by the rotorwinding.

Manuscript received March 3, 2010; revised July 26, 2010; acceptedSeptember 10, 2010. Date of publication September 30, 2010; date of currentversion July 13, 2011.

K. Hatua is with the Indian Institute of Science, Bangalore 560 012, India(e-mail: [email protected]).

V. T. Ranganathan, deceased, was with the Indian Institute of Science,Bangalore 560 012, India.

Digital Object Identifier 10.1109/TIE.2010.2081958

F Resultant flux flowing in themachine.

Ldc DC-link inductance.Lf Filter inductance at the excitation

winding.

Cf Per-phase filter capacitance at theexcitation winding.

isd,isq Resultant d- and q-axis statorcurrent of the active reactive in-duction machine (ARIM).

isdP,isqP/isdqP d- and q-axis power windingcurrents.

isdF,i

sqF d- and q-axis excitation windingcurrents referred to the power

winding.sr Rotor flux linkage in the station-

ary reference frame.

Lm Magnetizing inductance ofARIM.

LRR Rotor self-inductance.

isr Rotor current space vector in thestationary reference frame.

iSP Power winding current spacevector in the stationary reference

frame.iSF Excitation winding current space

vector in the stationary refer-

ence frame referred to the power

winding.

r Rotor time constant.RR Rotor resistance.mr Speed of rotor flux linkage space

vector in radians per second.slip Slip frequency in radians per

second.

e Electrical speed of the motor inradians per seconds.

md Developed electromagnetictorque of the motor.

P Number of poles of the motor.Kt Torque constant.isrP,isyP,isbP/isrybP Load-commutated inverter (LCI)

output currents.

irV SI,iyV SI,ibVSI/irybVSI Voltage source inverter (VSI)output currents.

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3374 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 58, NO. 8, AUGUST 2011

isrF,isyF,isbF/isrybF LCfilter output currents.srF,syF,sbF/srybF Excitation winding terminal

voltages.

srP,syP,sbP/srybP Power winding terminal voltages.ryb_grid Line-to-line voltages of the grid.Neq Equivalent turns ratio between

power and excitation windings.sdF,

sqF Excitation winding d- andq-axis voltages referred to thepower winding.

isdF,i

sqF Excitation winding d- andq-axis currents referred to thepower winding.

cos mr,sin mr Rotor flux position information.cos ,sin Power winding voltage position

vectors.

sP,sP/sP Power winding voltages in sta-tionary coordinate.

Lead angle required for safecommutation of thyristors in the

LCI.

tc Turnoff time required for safecommutation of thyristors in the

LCI.

Tch Change over time between theVSI and the LCI during starting.

f Reference of any parameter, e.g.,isq is theisqreference.

f Excitation winding voltages orcurrents referred to the power

winding.

i

sd_actF Theimr controller output.isd_lead d-axis current injected by the

LCI for proper commutation of

the silicon controlled rectifiers

(SCRs).

isd_total Total d-axis current injected bythe VSI.

iCSI_comp_d,iCSI_comp_q Out-of-phase dq componentsof the LCI-injected harmonic

currents.iCSI The LCI current space vector.esffdF,esffqF d- and q-axis feedforward terms

for the current controllers ofthe VSI.

Ur ,U

y ,U

b The LCI current unit vectors.

Ginv1Ginv6 Switching pulses for the LCI.Grec1Grec6 Switching pulses for the REC.

I. INTRODUCTION

THE following power topologies are popular for high-

power medium-voltage drives:

1) LCI-fed synchronous machine drives;

2) cycloconverter-based induction and synchronous ma-

chine drives for low-speed applications;

3) multilevel VSI-fed drives;4) cascaded H-bridge-fed drives.

Fig. 1. LCI-fed synchronous machine drive.

Fig. 2. LCI-fed induction motor drive.

Due to the advent of insulated-gate bipolar transistor

(IGBT), VSI technology became popular in low-voltage drives.

VSIs gradually replaced the thyristor-based CSI in ac machine

drives. Nowadays, multilevel VSI-fed topologies are becoming

popular for medium-voltage (10 MW) applications, the LCI-fedsynchronous motor drives are still very popular for simplicity,

reliability of the power hardware, and availability of the thyris-

tors (Fig. 1). In this drive, the field winding of a synchronous

machine is overexcited to ensure leading power factor at the

machine terminals. Thus, the thyristor switches of the LCI are

turned off without the help of any external commutation circuits

[15], [16].

Compared to a synchronous machine, an induction machine

is more rugged and cheaper and requires lesser maintenancedue to its simpler rotor structure. LCIs are not used in conjunc-

tion with induction machine because this machine presents a

lagging load to the inverter. Recently, it has been shown that, by

combining an LCI with a VSI, a new configuration can result

for a high-power induction machine drive (Fig. 2) [17][22].

The LCI carries the main power for the drive. The VSI with a

smaller power rating connected in the shunt path of the drive

ensures load commutation of the LCI by maintaining leading

power factor at the LCI output terminals. Moreover, the VSI

acts as a shunt active filter to compensate the LCI-injected

lower order harmonic currents and therefore ensures sinusoidal

motor currents and voltages. However, a transformer will be

required still at the VSI output terminal, provided that the motorterminal voltage is at a higher voltage (for example, 11 kV).

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HATUA AND RANGANATHAN: INDUCTION MOTOR DRIVE TOPOLOGY FOR MEDIUM-VOLTAGE DRIVE APPLICATIONS 3375

Fig. 3. Proposed LCI-fed ARIM drive.

VSI- and CSI-fed split-phase induction machine (SPIM)

drives are also popular for high-power applications [23][34].

The voltage ratings of switches become half compared to

switches for a three-phase drive. The sixth harmonic torque

pulsations are absent for CSI-fed SPIM drive.

A novel LCI-fed dual stator winding induction motor drive

topology is proposed in this paper (Fig. 3). The machine is

named as ARIM. ARIM contains two sets of three-phase wind-

ings with isolated neutral. Both the windings have a common

axis. One set of winding carries the active power and can

be wound for higher voltage (for example, 11 kV). Another

set supplies the total reactive power of the machine and can

be wound for lower voltage (for example, 2.2 kV). The rotor

is a standard squirrel cage. High-power induction machines

usually demand lesser magnitude of reactive power compared

to the total power rating of the machine (20%). Therefore, the

excitation winding has a smaller fraction of the total machine

rating compared to the power winding.

A VSI with an LC filter supplies reactive power to theARIM and ensures leading power factor at the power winding.

It is similar to the excitation control of the LCI-fed synchronous

machine. The direct VSI connection is possible due to the

lower voltage rating for the excitation winding. In this way,

the VSI voltage rating does not limit the highest motor voltagethat can be handled. An LCI supplies the real power into the

ARIM from the power winding. The LCI currents are quasi-

square wave in shape. Therefore, they have rich low-order

harmonic contents. They cause the sixth and twelfth harmonic

torque pulsations in the machine. This is a problem for LCI-

fed synchronous machine drive [35]. In the proposed drive,

the VSI can compensate these low-frequency MMF harmonics

inside the machine air gap to remove torque pulsation and rotor

harmonic losses.

This paper is organized in the following way. Section III

gives an overview of the machine, the power topology, and ba-

sic concept of the drive. Section IV contains the proposed con-trol technique. Section V deals with the experimental results.

Section VI deals with the converter ratings of the proposed

drive. Section VII concludes the paper.

II. BRIEFOVERVIEW OF THEM ACHINE, POWER

TOPOLOGY, A ND BASICC ONCEPT OF THED RIVE

A. Brief Overview of the Machine

The important feature of ARIM is the fact that the voltage

rating of both sets of windings can be decided independently,

which gives flexibility for power converter design. The kilo-

voltampere and voltage ratings of both the windings decide thecurrent rating of the windings.

Fig. 4. Conceptual diagram of ARIM.

ARIM behaves like a three-winding transformer. Fig. 4

shows the conceptual diagram of the ARIM. The rotor-induced

MMF (NR iR) is completely balanced by equal and op-posite MMF (NP iSP) of power winding. The flux of themachine(F) is generated only by the MMF (NF iSF) ofthe excitation winding. This is achieved by the proposed control

technique, which will be discussed in Section IV.By adjusting the number of turns of the excitation winding,

the voltage and current ratings of this winding can be decided.

The voltage rating of this winding should be decided to facil-

itate direct VSI connection with the excitation winding. This

adjustment is independent of power winding.

The MMFs of both stators add up vectorially in the air gap. It

is the resultant MMF which is responsible for the induced rotor

voltage and torque production.

B. Power Converter Topology and Basic Concepts

of the ARIM Drive

Fig. 5 shows the power schematic for ARIM drive. A1B1C1

is designated as the excitation winding, whereas A2B2C2 is

designated as the power winding. A1B1C1 winding is con-

nected to an IGBT-based VSI via an output LC filter. TheVSI supplies the total reactive power to the motor. The flux

winding can be wound up to a convenient voltage level to

avoid a transformer between A1B1C1 winding and VSI for

stepping up the voltage. The LCfilter makes the VSI outputvoltage sinusoidal. The VSI also supplies a small amount of

field axis current to ensure leading power factor at the power

winding. A2B2C2 winding is connected to a thyristor-based

LCI. LCI injects the fundamental component of the powerwinding current. It injects quasi-square wave current into the

motor. The LCI is switched at fundamental frequency of the

motor voltage. It supplies the total active power to the motor.

A2B2C2 winding can be designed for a higher voltage level as

required by the motor; the thyristor-based LCI can be directly

connected to it. As the VSI ensures leading power factor at the

power winding terminals, the thyristor switches of the LCI are

turned off by the load commutation process that is similar to

the LCI-fed synchronous machine drive. The thyristor-based

rectifier REC and dc-link inductor(Ldc)generate a controlleddc-link current.

The LCI also injects lower order harmonics into the machine.

They cause the sixth harmonic torque pulsation in the machineif not compensated. For LCI-fed synchronous motor drives,

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Fig. 5. Power hardware for ARIM drive.

this is a major drawback. In the proposed drive, the sixth

harmonic torque pulsation can be avoided by injecting opposite

phase harmonic currents from the VSI. Although lower order

harmonics will be present in the LCI current, they will be

magnetically cancelled inside the machine by the VSI current.

III. PROPOSEDC ONTROLT ECHNIQUE

In this section, the proposed control topology for the ARIM

is discussed. The basic objectives are as follows.

1) Supply active power of the motor from the LCI and

reactive power from the VSI.

2) Ensure load commutation in the LCI, maintaining leading

power factor at its terminal.

3) Compensate low-order harmonics injected from the LCI

with the help of VSI to avoid torque pulsations.

To achieve the aforementioned goals, the machine is modeled

in the rotor flux coordinate system.

A. Modeling of ARIM in Rotor Flux Reference Frame

Modeling of the ARIM follows an approach similar to that

of the SPIM [34]. The MMFs produced by both sets of stator

windings add up vectorially in the air gap. The resultant flux

generated by them links the rotor.

Therefore, the rotor cannot distinguish the stator MMF pat-

terns of both the windings separately. Rather, it sees the flux as

if generated from a single three-phase winding. For simplicity

of the control, voltages and currents of the excitation windings

are referred to the power winding.

The resultantd-axis stator current(isd)is the algebraic sumofd-axis power winding (isdP) and referred d-axis excitationwinding (isdF) currents. Similarly, the resultant q-axis statorcurrent (isq) is the algebraic summation of two components:One is the q-axis power winding current (isqP), and thesecond one is the referred q-axis excitation winding (isqF)current. Equations (1) and (2) mathematically elaborate the

relationships

isd= isdP+ i

sdF (1)

isq = isqP+ i

sqF. (2)

The rotor flux linkage( sr )in the stationary reference framecan be expressed as follows:

sr =Lm

iSP+i

SF

+ LRRi

sr =Lmi

smr. (3)

The rotor voltage equation and the torque equation in the

rotor flux coordinate system are expressed in

(isdP+ i

sdF) = imr+ r(d/dt)imr

r =LRR/RR (4)

isqP+ i

sqF = rslipimr (5)

mr = (slip+ e) (6)

md=Kt imrisqP+ i

sqF

Kt= (2/3) (P/2) L2m/LRR

. (7)

From (4), it can be inferred that, at steady state, the imr ofthe machine can be supplied from both thed-axis power(isdP)and referred excitation winding (isdF) currents. Therefore,setting the d-axis current reference of the power winding tozero(isdP = 0), the total rotor flux demand can be met fromthe excitation winding current alone. Similarly, from (7), it

can be interpreted that the torque component of current is the

algebraic summation ofq-axis power current(isqP)and q-axiscurrent i

sqFof the excitation winding. Therefore, setting the

q-axis current reference of flux winding to zero (isqF = 0), thetotal torque-producing current can be supplied from the power

winding alone.

B. Description of Control Block Diagram

The proposed control technique (Fig. 6) follows a vector

control topology. The voltages and currents of the excitation

winding are referred to the power winding side for the sim-

plicity of control. The control algorithm is subdivided into the

following modules:

1) estimation;

2) VSI control scheme;

3) CSI control scheme;

4) rectifier control scheme.

1) Estimation: The BLOCK I in Fig. 6 elaborates the es-

timation module of the proposed control scheme. imr andslip are estimated from (4) and (5), respectively. The elec-trical speed (e) of the motor is measured from the speedencoder mounted on the motor shaft. The mr of the motoris calculated from (6). The position information of the rotor

flux (cos mr, sin mr) is obtained from the information ofmr. The position information (cos , sin ) of the terminalvoltages of the power winding is required to generate the LCI

firing pulses. The voltages(sP, sP) are integrated with alow-pass filter (LPF) having a cutoff frequency of around 5 Hz

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Fig. 6. Control block diagram.

to eliminate the motor terminal voltage noises from the position

information(cos , sin ). The filter is introduced to eliminatedc drift problems faced in the process of pure integration.

2) VSI Control Scheme: A two-level VSI with anLCfilteris connected with the excitation winding (A1B1C1). The fol-

lowing functions are carried out by it:

1) supply of reactive power to the excitation winding of theARIM;

2) ensuring leading power factor at the power winding ter-

minals with a defined lead angle ();3) elimination of the sixth harmonic torque pulsation in the

machine;

4) active damping of resonating component of the machine

terminal voltage due to the presence ofLCfilter.

The BLOCK II in Fig. 6 elaborates the VSI control scheme

of the proposed control technique. The imr controller of theARIM generates the d-axis current reference (isd_actF). TheVSI supplies the total d-axis current to maintain the required

flux level(imr)in the machine. The VSI also injects additionalcurrent(isd_lead)into the machine to maintain a lead angle

at the CSI terminal, along with isd_actF. This is similar to theoverexcitation of the synchronous machine. The unit vectors

of the stator voltage are phase advanced by to generate theunit vectors of the CSI current. The resulting component of the

CSI current along the negative d-axis is compensated by addingit to the d-axis current reference (isd_lead) produced by imr

controller.isd_total is the total current injected by the VSI, i.e.,

isd_total = isd_actF isd_lead. (8)

The LCI supplies quasi-square wave currents in the ARIM.

They are rich in lower order harmonics (fifth, seventh, eleventh,

thirteenth, etc.). They develop unwanted sixth and twelfth har-

monic torque pulsations and increase rotor copper loss. This

is a serious problem in LCI-fed induction machine drives and

the LCI-fed synchronous machine drive. Interestingly, they

can be completely compensated in the proposed drive. The

LCI harmonic currents(iCSI_comp_d,iCSI_comp_q)are es-timated using LPFs. The out-of-phase LCI harmonic currents

(iCSI_comp_d, iCSI_comp_q) are also supplied by the VSI. Bythis control action, the LCI and VSI harmonic currents cancel

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Fig. 7. Vector diagram.

each other in the air gap, and unwanted low-frequency torque

pulsations and rotor harmonic copper losses are eliminated

from the proposed drive. It is to be noticed that, in the LCI-fed

synchronous machine drive, the LCI-injected low-frequencyharmonic components cannot be canceled by harmonic injec-

tion from the rotor.

TheLC filter in the excitation winding causes motor terminalvoltage oscillations at resonant frequency. By active-damping

technique, they can be eliminated. The active-damping tech-

nique does not change the design of the main control loop.

The compensating signals for active damping are injected with

the feedforward terms (esffdF, esffqF) in the current controlloops.

3) LCI Control Scheme: The LCI supplies active power

to the ARIM. The BLOCK III in Fig. 6 elaborates the LCI

control scheme of the proposed control technique. The LCI is

switched at fundamental frequency of the motor voltages to

supply quasi-square wave currents in the ARIM. The thyristors

of the LCI are load commutated. To obtain load commutation of

the thyristors in the LCI, phase currents of the power winding

have to lead the corresponding per-phase voltages by an angle

(). The thyristors used in the LCI are converter grade. tcis thecommutation time required for safe turnoff of thyristors. The angle is determined by

= mrtc. (9)

Fig. 7 shows the LCI current and machine terminal voltage

space vectors. dq axes represent the rotor flux axes, anddq axes represent the power winding voltage axes. Thepower winding voltage position (cos , sin ) is determinedfrom the Estimation block in Fig. 6. UCSI and U

CSI are

generated by the leading angle with respect to the voltageunit vectors (cos , sin ). LCI current unit vectors (Ur , U

y , U

b )are obtained by two-to-three-phase transformation ofUCSIandUCSI. The unit amplitude LCI unit vectors are comparedwith 0.5 to generate the switching pulses (Ginv1Ginv6) forthyristors of the LCI, with a phase shift of 30 from the zero

crossings of the CSI current unit vectors.

4) Rectifier Control Scheme: The dc-link current required

for the control is generated by a thyristor-based rectifier and

a dc-link choke. The BLOCK IV in Fig. 6 elaborates therectifier control schemeof the proposed control technique. The

Fig. 8. Starting of the ARIM.

speed controller output generates the required isq. The dc-linkcurrent reference(idc)is obtained by summingi

sqand isd_leadvectorially. The dc-link controller output gives the firing angle

information (cos) for the rectifier. With the help of gridline-to-line voltage (ryb_grid) information and firing angleinformation (cos), the rectifier firing pulses (Grec1Grec6)are generated.

5) Starting of the ARIM: At very low speeds of the machine,

the terminal voltages are also very low. Their magnitudes are

not sufficient to switch off the thyristors in the LCI. There-

fore, ARIM is started with the VSI, until the mr of themachine reaches 5 Hz. Fig. 8 describes the changeover process.

Conventional vector control topology is adopted in this mode

(MODE 1) of operation. The LCI does not operate in

MODE 1. When the mr of the machine crosses 5 Hz at timeTch, the i

sqF of the VSI is slowly reduced to zero, and the

q-axis LCI current reference(iCSIq)is increased up to the speedcontroller output(isq).

During this mode (MODE 2) of operation, the active power

is shared by both the VSI and the LCI. At the end of MODE 2,

the LCI supplies the total active power, and the VSI supplies

the total reactive power of the machine. This mode is termed

as MODE 3. The ARIM is operated at higher speeds(mr >5Hz) in MODE 3. In this way, the active power is transferredfrom the VSI to the LCI.

IV. EXPERIMENTALR ESULTS

A 5.5-kW ARIM with 415-V power winding and 220-V

excitation winding is designed for proving the concept. The

machine details are given in the Appendix. Due to the un-

availability of the manufacturer of medium-voltage machine,

the concept is proved on a low-voltage prototype. However, the

concept can be implemented for medium-voltage machine.The

excitation winding is connected to a two-level IGBT-based VSI

with anLCfilter. Filter details are also given in the Appendix.Power winding is connected to a thyristor-based LCI. LCI is

connected with a thyristor-based rectifier via a dc-link choke.

The experiment is carried out on a hybrid digital platform. The

hybrid board has a TMS 320LF 2407A DSP processor and an

ALTERA CYCLONE FPGA processor.

A. Steady-State Waveforms

Figs. 912 show the steady-state waveforms of the proposed

ARIM drive. The Ch 1 in Fig. 9 is the A2B2 power winding

line-to-line voltage. Ch 2 is the A1 winding phase voltage.

At steady state, the Ch1 voltage leads the Ch2 voltage almost

by 30. At steady state, the per-phase voltage of both sets ofwindings will have almost zero-degree phase difference since

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Fig. 9. Steady-state waveform at 42 Hz with compensation. (Ch1) Powerwinding line-to-line (A2B2) voltage (800 V/div). (Ch2) Excitation windingphase (A1) voltage (800 V/div). (Ch3) Excitation winding line current (A1)(20 A/div). (Ch4) Power winding line current (A2) (10 A/div). Time=20ms/div.

Fig. 10. Steady-state waveform at 35 Hzwithout compensation. (Ch1) Exci-tation winding phase (A1N) voltage (160 V/div). (Ch2) Excitation winding linecurrent (A1) (15 A/div). (Ch3) Power winding line current (A2) (10 A/div).(Ch4) Developed torque (10 N

m/div). Time = 10ms/div.

Fig. 11. Steady-state waveform at 35 Hzwith compensation. (Ch1) Excitationwinding phase (A1N) voltage (160 V/div). (Ch2) Excitation winding linecurrent (A1) (15 A/div). (Ch3) Power winding line current (A2) (10 A/div).(Ch4) Developed torque (10 Nm/div). Time = 10ms/div.

there is no spatial gap present between both sets of windings.

The Ch3 in Fig. 9 is the excitation winding current. It lags the

Ch2 voltage almost by 90, as it carries only the reactive power

of the machine. The Ch 4 in Fig. 9 is the A2 winding LCI line

current. It leads the Ch2 voltage by the angle (= 15) forproper commutation of the SCRs. The Ch 4 in Figs. 10 and

11 are the estimated torques of the machine. In Fig. 10, torque

compensation from the flux winding is not carried out. There-fore, the steady-state torque (Ch 4) contains harmonic torque

Fig. 12. Voltage across a thyristor of LCI. (Ch1) Voltage (VT1) across athyristor (T1) of the CSI (160 V/div) (see Fig. 5). (Ch2) Zoomed portion ofCh1. Time = 100ms/div for Ch1 and 10 ms/div for Ch2.

Fig. 13. Speed change from 10 to 42 Hz. (Ch1) Power winding line-to-line(A2B2) voltage (800 V/div). (Ch2) A1 phase CSI current (10 A/div). (Ch3)

Speed reference of the machine (800 r/min/div). (Ch4) Actual machine speed(800 r/min/div). Time = 1s/div.

pulsations. On the contrary, the steady-state torque (Ch 4)

in Fig. 11 is smoother since excitation winding compensates

for the torque pulsations. Fig. 12 shows the voltage across a

thyristor. In Ch 2 of Fig. 12, beta is the angle responsible for

load commutation. This voltage has to be negative during the

commutation process for proper turnoff of the thyristors.

B. Dynamic Waveforms

Fig. 13 shows the speed response of the drive. Figs. 14 and

15 show the response of the drive during a sudden load change.isd_lead is the d-axis projection ofiCSI. Therefore, when theload is applied across the machine, then the isd_lead of themachine increases also with the load. Therefore, the excitation

winding has to inject more reactive power into the machine

compared to the no-load condition. The Ch 3 in Fig. 14 is the

iSF d signal of the machine. Its magnitude increases with theload. Fig. 15 shows the dc-link current signal of the drive during

a sudden load change.

C. Starting of the ARIM

ARIM is started with the VSI from the excitation winding.

LCI supplies the active power after the machine speed reaches5 Hz. The Ch4 in Fig. 16 shows the LCI current during starting.

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Fig. 14. Sudden application of the load torque. (Ch1) Power winding line-to-line (A2B2) voltage (400 V/div). (Ch2) A1 phase CSI current (10 A/div).(Ch3) i

SFdsignalof themachine (5 A/div). (Ch4) Applied load on themachine

(1.5 kW/div). Time = 500ms/div.

Fig. 15. DC-link current response during a sudden load change. (Ch1) Power

winding line-to-line (A2B2) voltage (800 V/div). (Ch2) A1 phase CSI current(10A/div). (Ch3) DC-link current (5 A/div). (Ch4) Applied load on themachine(1.5 kW/div). Time = 500ms/div.

Fig. 16. Starting of the ARIM. (Ch1) Power winding line-to-line (A2B2)voltage (25 V/div). (Ch2) Excitation winding phase (A1) voltage (25 V/div).(Ch3) Excitation winding line current (A1) (20 A/div). (Ch4) Power windingline current (A2) (10 A/div). Time = 200ms/div.

V. DISCUSSIONS ONC ONVERTERR ATINGS

The total power required by the motor is shared between the

VSI and the LCI. The LCI carries active power while the VSI

carries reactive power of the machine. The LCI and VSI ratings

of the proposed ARIM drive are calculated for an ARIM having

total kilovoltampere, active power, and reactive power in theratio of 1 : 0.98 : 0.2 and power winding to excitation winding

TABLE ICONVERTER RATINGS

voltage in the ratio of 5 : 1. The power winding voltage and the

kilovoltampere of the machine are chosen as per-unit bases.

Case 1Without Harmonic Compensation From the Excita-

tion Winding: In Case 1, the currents in the power winding

are in the same phase with the corresponding phase voltages

(except the small lead required for commutation). Therefore,

the fundamental current magnitude is the ratio between the

real power handled by a phase of power winding and the

corresponding phase voltage. The net rms current supplied by

the LCI is /3 times that of the fundamental current of thecorresponding winding. Therefore, the LCI current rating is

(/3)

0.98 = 1.03 p.u. The VSI voltage rating is 0.2 p.u.because the power winding to excitation winding voltage ratiois 5 : 1. The excitation winding draws a current of 1 p.u. to

maintain the net MMF balance of the machine.

Case 2With Harmonic Compensation From the Excitation

Winding: In Case 2, the excitation winding supplies compen-

sating harmonic currents along with the fundamental reactive

currents. Therefore, the current rating of the VSI is more

compared to the previous case. All other ratings remain the

same. Table I gives a description for different converter ratings.

VI. CONCLUSION

In this paper, a new power topology for high-power medium-voltage drive has been proposed. The proposed drive can be

used in pump, fan, and compressor types of load. The benefits

of the proposed drive are manifold over the existing technolo-

gies, namely, multilevel VSI-fed drives, LCI-fed synchronous

machine drive, etc. The proposed drive exploits the benefits of

both thyristors and IGBTs to find an attractive solution for high-

power medium-voltage drive applications. As the proposed

machine, ARIM is an induction machine; it is more rugged,

maintenance free, and cheaper compared to a synchronous

machine. The active power of the drive is handled by the LCI.

Thyristors for the LCI are available more easily compared to

high-power IGBTs used in the VSI technology. Moreover, theabsence of any transformers in the proposed drive makes it

very attractive. In the proposed drive, the sixth harmonic torque

pulsations can be avoided, unlike the LCI-fed synchronous

machine drives.

Speed reversal and regeneration can also be implemented

in the proposed drive. The proposed ARIM drive can offer

numerous advantages in high-power applications.

APPENDIX

5.5-kW four-pole 50-Hz 1440-r/min ARIM

Power winding: 415 V, 8.37 A

Excitation winding: 220 V, 10.8 AFilter Parameters:Lf = 4mH andCf = 10F

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DC-link Inductor:Ldc= 180mHMachine Parameters:

Power winding resistanceRSP = 1.5 Referred excitation winding resistanceRSF = 2.4 Power winding leakagePLSSP = 0.76mHReferred excitation winding leakageFLSSF = 2.04mH

Leakage between power and excitation windingsLlsm = 2mH

Lm= 138.13 mH, Llr = 7.34 mH, RR= 0.743 ,LRR = 145.47mH.

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Kamalesh Hatua was born in Kolkata, India, in1976. He received the B.E. degree in electrical andelectronics engineering from Karnataka RegionalEngineering College, Surathkal, Mangalore, India,in 2000 and the M.Sc. degree in electrical engineer-ing from the Indian Institute of Science, Bangalore,India, in 2004, where he is currently working towardthe Ph.D. degree.

After he obtained his B.E. degree, he was withBharat Earth Movers, Ltd., Mysore, India. After he

obtained his M.Sc. degree, he was with HoneywellTechnology Solutions Laboratory, Bangalore, where he worked on the develop-ment of inverter for aerospace applications.

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V. T. Ranganathan (M86SM92) was born inChennai, India, in 1955. He received the B.E. andM.E. degrees in electrical engineering from theIndian Institute of Science (I.I.Sc.), Bangalore, India,in 1977 and 1979, respectively, and the Ph.D. degreefrom Concordia University, Montreal, QC, Canada,in 1984.

He joined the Electrical Engineering Department,

I.I.Sc., in 1984 as an Assistant Professor, where hewas a Professor. His research interests were in theareas of power electronics and motor drives. He

has made significant research contributions in the areas of vector controlof ac drives, pulsewidth-modulation techniques, split-phase induction motordrives, and slip-ring induction motor drives. His work had led to a numberof publications in leading journals, as well as patents. He was also active asa Consultant to industry and had participated in a number of research anddevelopment projects in various areas, such as industrial drives, servodrives,traction drives, wind energy, and automotive applications. He passed away onDecember 30, 2010.

Dr. Ranganathan was the recipient of a Prize Paper Award from the Sta-tic Power Converter Committee of the IEEE Industry Applications Society(in 1982), the Tata Rao Prize of the Institution of Engineers India (in19911992), the VASVIK Award in Electrical Sciences and Technology (in1994), the Bimal Bose Award of the Institution of Electronics and Telecommu-nication Engineers, India (in2001), andthe C. V. Raman Young ScientistAward

of the Government of Karnataka and the Rustom Choksi Award for Excellencein Engineering Research (in 2005) in the I.I.Sc. He is a Fellow of the IndianNational Academy of Engineering and the Institution of Engineers.

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